Morphogens 1 Flashcards

1
Q

What gene was identified as being abundant in the head region of Xenopus embryo?

A

Cerberus (three headed dog!).

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2
Q

What does injection of cerberus into vegetal blastomeres cause?

A

Ectopic head structures but no secondary axis.

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3
Q

What is the primary function of cerberus in the developing embryo?

A

To inhibit nodal, BMP, and Wnt signalling. This allows head formation.

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4
Q

What happens during Xenopus development if we knock down cerberus? What about if we also knock down Dickkopf and Frzb?

A

Nothing, because of redundancy. Triple-knockdown results in a loss of head structures.

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5
Q

How is β-catenin involved in Wnt signalling?

A

When Wnt is active, β-catenin is free to migrate to the nucleus where it acts as a transcription factor.

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6
Q

What is the general role of Wnt signalling when specifying the Xenopus body plan?

A

To act as a trunk inducer.

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7
Q

What gene along the anterior-posterior axis at the neural plate stage is later expressed in the forebrain?

A

Krox20.

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8
Q

What gene along the anterior-posterior axis at the neural plate stage is later expressed in the forebrain and midbrain?

A

Otx2.

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9
Q

What gene along the anterior-posterior axis at the neural plate stage is later expressed in the hindbrain?

A

Bf1.

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10
Q

How did researchers show that Wnt was functioning in a concentration-dependent manner in the embryo?

A

They dissociated tissues and then exposed them to varying concentrations of Wnt, observing different tissue fates.

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11
Q

What morphogen gradient patterns the Xenopus anterior-posterior axis?

A

Wnt gradient.

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12
Q

What are the 2 criteria which must be satisfied for something to be acting as a morphogen?

A
  1. Forms a gradient of concentration

2. Different concentrations induce varied responses

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13
Q

What model tries to explain the idea that varying concentrations of a morphogen have sharp cutoff values in terms of tissue fate specification?

A

The French flag model.

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14
Q

What 2 adjacent tissues influence fate of cells in the neural tube?

A
  1. Ectoderm

2. Notochord

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15
Q

What differentiates the eventual function of the dorsal neural tube from the ventral neural tube?

A

Dorsal: receives signals from the PNS receptors (pain, touch, etc.)
Ventral: innervates the motor neurons

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16
Q

What programs the motor neurons of the ventral neural tube?

A

The central pattern generator.

17
Q

What factor is being secreted from the notochord as a morphogen to determine neural tube cell fate?

A

Sonic hedgehog (Shh)!

18
Q

What does “combinatorial coding” mean in terms of neuronal cell-type specification?

A

It means overlapping morphogens are responsible for cell differentiation, rather than a single factor specifying a specific fate.

19
Q

What advantage does combinatorial coding have over direct cell fate specification?

A

It’s economical. A small number of TFs can give rise to a large number of expression domains.

20
Q

How does zebrafish neurulation differ from mammalian neurulation?

A

Mammal: neural plate hinges into open tube
Zebrafish: neural plate expands into closed “neural keel” before opening an internal lumen.